function [B_next] = update_B(X_t,T, At, Zt )
%UPDATE_Z 此处显示有关此函数的摘要
%   此处显示详细说明
Tmp = T'*Zt'*At*X_t;
[Up,Sp,Vp] = svd(Tmp,'econ');
B_next = Up*Vp';
%  B_next'*B_next 
%  B_next*B_next'
% 正交 B_next'*B_next
% Tmp = T_last'*Pt'*Z_last'*At*Xt;
% size(Tmp)
% [Up,Sp,Vp] = svd(Tmp,'econ');
% B_next = Up*Vp';
% size(B_next)
% 正交 B_next*B_next'
end
